Adaptive medium voltage therapy for cardiac arrhythmias

ABSTRACT

Aspects of the invention are directed to advanced monitoring and control of medium voltage therapy (MVT) in implantable and external devices. Apparatus and methods are disclosed that facilitate dynamic adjustment of MVT parameter values in response to new and changing circumstances such as the patient&#39;s condition before, during, and after administration of MVT. Administration of MVT is automatically and dynamically adjusted to achieve specific treatment or life-support objectives, such as prolongation of the body&#39;s ability to endure and respond to MVT, specifically addressing the type of arrhythmia or other pathologic state of the patient with targeted treatment, a tiered-intensity MVT treatment strategy, and supporting patients in non life-critical conditions where the heart may nevertheless benefit from a certain level of assistance.

PRIOR APPLICATION

This Application is a divisional of U.S. patent application Ser. No.12/830,251, filed Jul. 2, 2010 (Now U.S. Pat. No. 8,483,822), whichclaims the benefit of U.S. Provisional Application No. 61/270,124, filedJul. 2, 2009, entitled “Method and Apparatus for Providing PerfusionDuring VF, PEA and Asystole in External and Implantable CardiacDevices,” and further identified in its Application Data Sheet as“Medium Voltage Therapy for the Treatment of Cardiac ArrhythmiasIncluding Pulseless Electrical Activity, Asystole and VentricularFibrillation,” and which is incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to treatments for individualsexperiencing cardiac arrest and, more particularly, to implantable orexternal treatment apparatus and associated methods of operationthereof, for improving the applicability and effectiveness of mediumvoltage therapy (MVT) for a variety of patient conditions.

BACKGROUND OF THE INVENTION

Cardiac arrest is a significant public health problem cutting acrossage, race, and gender. A positive impact on cardiac arrest survival hasbeen demonstrated with the substantial reduction in time todefibrillation provided by the widespread deployment of automatedexternal defibrillators (AEDs), and the use of implantable cardioverterdefibrillators (ICDs) and implantable pulse generators (IPGs). Examplesof AEDs are described in U.S. Pat. Nos. 5,607,454, 5,700,281 and6,577,102; examples of ICDs are described in U.S. Pat. Nos. 5,391,186,7,383,085, and 4,407,288, and examples of IPGs are described in U.S.Pat. Nos. 4,463,760, 3,978,865, and 4,301,804, the disclosures of whichare incorporated by reference herein.

Optimal resuscitation therapy for out of hospital (OOH) cardiac arrestis the subject of substantial ongoing research. Research has been clearin demonstrating that the timing of resuscitation is of criticalimportance. For example, there is less than a 10% chance of recoveryjust ten minutes after the onset of ventricular fibrillation (VF). Thisknowledge led to the recent widespread deployment of AEDs, primarily inpublic areas with a high population concentration such as airports andshopping malls. A positive impact on cardiac arrest survival has beendemonstrated due to the substantial reduction in time to defibrillationas a result of more available access to AEDs. In addition, for thosepatients identified as being at particularly high risk, an implantablecardioverter-defibrillator is often implanted in order to addressepisodes of cardiac arrest without the involvement of a rescuer.

In the case of VF, performing CPR-type chest compressions beforedefibrillation and minimizing the time to defibrillation shock followingthe cessation of the CPR chest compressions is important in facilitatingeffective recovery especially in cases of long duration VF. It isgenerally believed that perfusion of the myocardium achieved during CPRpreconditions the heart for the defibrillating shock. Despite theimportance of CPR, it is often not performed in the field for a varietyof reasons.

Cardiac electrotherapy stimuli having an amplitude that is greater thanthat of pacing-type stimuli, but less than the amplitude and energylevel associated with defibrillation-type stimuli, are known in the artas medium voltage therapy (MVT). For example, U.S. Pat. No. 5,314,448describes delivering low-energy pre-treatment pulses followed byhigh-energy defibrillation pulses, utilizing a common set of electrodesfor both types of stimuli. According to one therapeutic mechanism ofthis pre-treatment, the MVT pulses re-organize the electrical activitywithin the cardiac cells of the patient to facilitate a greaterprobability of successful defibrillation with a follow-on defibrillationpulse. U.S. Pat. No. 6,760,621 describes the use of MVT as pretreatmentto defibrillation that is directed to reducing the likelihood ofpulseless electrical activity and electromechanical dissociationconditions as a result of the defibrillation treatment. The mechanism bywhich these results are achieved by MVT has been described as a form ofsympathetic stimulation of the heart. These approaches are directed toinfluencing the electrochemical dynamics or responsiveness of the hearttissues.

MVT has also been recognized as a way of forcing some amount of cardiacoutput by electrically stimulating the heart directly with stimuli thatcause the heart and skeletal muscles to expand and contract in acontrolled manner. See U.S. Pat. Nos. 5,735,876, 5,782,883 and5,871,510. These patents describe implantable devices having combineddefibrillation, and MVT capability for forcing cardiac output. U.S. Pat.No. 6,314,319 describes internal and external systems and associatedmethods of utilizing MVT to achieve a hemodynamic effect in the heart aspart of an implantable cardioverter defibrillator (ICD) for purposes ofachieving a smaller prophylactic device. The approach described in the'319 patent uses the MVT therapy to provide a smaller and less expensiveimplantable device that can maintain some cardiac output withoutnecessarily providing defibrillation therapy.

Unlike a conventional defibrillator or an IPG, which operates with theprimary purpose of restoring a normal cardiac rhythm, MVT stimulationcan be used to provide cardiac output, which in turn causes perfusion tothe heart and brain, as well as other critical body tissues. Byproviding perfusion to the heart and other vital organs, MVT prolongsthe life of the patient even while the patient continues experiencingthe arrhythmia. Additionally, MVT improves the likelihood of successfuldefibrillation or of a spontaneous return of circulation. In anotherapplication, MVT may be utilized to place a heart into a distended stateby continuing venous return in the absence of cardiac output, thusmaking it more likely to return to a spontaneous pulsatile rhythm. AnAED equipped with MVT can provide consistent high quality chestcompressions. In the case of an implanted ICD or IPG, back up chestcompressions provided by MVT can, in one sense, be even more importantthan in an external, since in the case of the implantable device theremay be no rescuer available to perform CPR when needed.

Recent studies have identified an increasing incidence of patients whoseinitial rhythm is not VF, but may be (PEA), or asystole. In addition inmany cases an unsuccessful defibrillation shock (whether from an AED oran ICD) results in PEA, asystole or persistent VF. In all these casesthe indicated therapy is CPR type chest compressions. Conventional ICD,IPG, and AED devices, even those enabled with MVT, work very well totreat VF, but provide little or no therapy for other common arrhythmiasof cardiac arrest, namely, pulseless electrical activity (PEA) andasystole.

While developments in defibrillator technology, both automatic externaldefibrillators (AEDs) and implantable cardioverter defibrillators (ICDs)have made great strides in aiding the electrical cardiac resuscitationof individuals experiencing cardiac arrest, a need exists for a solutionthat can effectively treat the increasing number of victims that eitherpresent with non-VF cardiac arrest or are shocked into a non-VFnon-pulsatile rhythm such as PEA or asystole.

U.S. Pat. No. 8,401,637 describes a technique and associated apparatusthat combines defibrillation therapy with MVT into an external devicehaving a capability to perform electrical CPR. Externally-applied MVT isproposed for stimulating skeletal and sympathetic muscles in addition tomyocardial muscle tissue to effect chest compression and evenventilation in the patient. The '637 patent reflects the knowledge inthe art that due to the inclusion of differing time constant componentsin an MVT waveform, the waveform can stimulate contraction of a varietyof different types of muscles, e.g., myocardial, skeletal, sympatheticmuscles, and the phrenic nerve. Varying and controlling the MVT waveformparameters, including variation of the musculature targeted by thewaveform, is described as a way to maximize coronary perfusion pressuregenerated by application of MVT.

Notwithstanding the advancements in MVT for cardiac output forcing madeto-date, known MVT techniques have been shown to be effective for only alimited time due to muscle fatigue resulting from application of theMVT. Particularly, after repeated application of the MVT electricalpulses, the muscles being stimulated become unresponsive to further MVTstimulation, resulting in a drop-off in coronary perfusion. A solutionis therefore needed for enabling longer duration and more productive MVTsessions.

SUMMARY OF THE INVENTION

One aspect of the invention is directed to advanced monitoring andcontrol of medium voltage therapy (MVT) in implantable and externaldevices. Apparatus and methods are disclosed that facilitate dynamicadjustment of MVT parameter values in response to new and changingcircumstances such as the patient's condition before, during, and afteradministration of MVT. MVT is selectively targeted to specific musclesusing variation of waveform characteristics, and/or using specificlocation-based targeting. The MVT is applied and adjusted based onmonitored patient condition information, including monitored hemodynamicinformation. Administration of MVT is automatically and dynamicallyadjusted to achieve specific treatment or life-support objectives. Onesuch objective is prolongation of the body's ability to endure andrespond to MVT. Other objectives are specific to the type of arrhythmiaor other pathologic state of the patient.

In another aspect, advanced monitoring techniques are applied to detectand treat specific conditions, such as pulseless electrical activity(PEA), for example. In one type of embodiment, MVT treatment electrodesare utilized to make hemodynamic measurements. In one particularexample, hemodynamic measurements are made concurrently with theadministration of the MVT. In another type of embodiment, theadministration of MVT is controlled such that the MVT is synchronizedwith the ECG of a PEA condition.

In another aspect, methods and apparatus are described for administeringa multi-tier MVT treatment algorithm, to be carried out by animplantable or external MVT-enabled device. The device according to oneembodiment is configured to apply a higher intensity MVT at certainstages of rescue or life support, and to apply a lower intensity MVT atother stages. The intensity of MVT is varied by adjusting certain MVTparameters in response to a monitored condition of the patient.Higher-intensity and lower-intensity MVT may be selectively applieddifferently between MVT targeting the heart and MVT targeting theskeletal muscles, depending on the treatment objective, which in turndepends on the detected patient condition obtained using the patientmonitoring facilities of the device.

In another aspect of the invention, adaptive MVT is applied to supportpatients in non life-critical conditions but where the heart may benefitfrom a certain level of assistance, such as orthostatic hypotension, forexample. Hemodynamic monitoring and ECG measurements are used toidentify such conditions, and to control proper administration of theMVT.

A number of advantages will become apparent from the following DetailedDescription of the Preferred Embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating the sub-systems of an implantabledevice enabled with medium voltage therapy (MVT) facilities, accordingto one embodiment.

FIGS. 2A-2C illustrate various examples of electrode arrangements forimplantable MVT devices such as the device of FIG. 1 according tovarious embodiments.

FIG. 3A is a diagram illustrating the sub-systems of an external deviceenabled with medium voltage therapy facilities, according to oneembodiment.

FIG. 3B is a diagram illustrating an exemplary operator interface of thedevice of FIG. 3A.

FIG. 3C is a diagram illustrating various examples of electrodes andsensors of the patient interface of the device of FIG. 3A.

FIGS. 4A-4B are time-domain waveform diagrams illustrating variableparameters of the MVT according to various embodiments of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram illustrating an implantable MVT device 10constructed in accordance with one aspect of the invention. The devicecircuitry is electrically coupled with regions of the patient's upperbody 40 via a series of leads—output lead 32, pressure sense lead 34,and ECG sense lead 36. The electronic circuit includes a conventionalECG amplifier 30 for amplifying cardiac signals. The amplified cardiacsignals are analyzed by a conventional arrhythmia detector 20 whichdetermines if an arrhythmia is present. The arrhythmia detector 20 maybe one of several types well known to those skilled in the art and ispreferably able to distinguish between different types of arrhythmias.For example; fibrillation, tachycardia, asystole.

The exemplary circuit also contains a hemodynamic sensing section 28which amplifies and conditions a signal from a one or more hemodynamicsensors such as, for example, a pressure sensor within the heart orartery, such as the pressure sensor described in U.S. Pat. No.6,171,252, the disclosure of which is incorporated by reference herein.Another type of hemodynamic sensor that can be used in an implantableembodiment is a microphone and associated processing device formonitoring audible body sounds (much like an indwelling stethoscope)indicative of blood flow as described in U.S. Pat. No. 7,035,684, thedisclosure of which is incorporated by reference herein. Yet anothersuitable hemodynamic sensing technique is one featuring an ultrasonicblood flow sensor, such as the Doppler pulse sensor described in U.S.Pat. No. 4,823,800, the disclosure of which is incorporated by referenceherein. Still another hemodynamic sensing technique that may be employedis impedance plethysmography (tomography) in which a series ofelectrodes are placed to measure changing impedance in localized regionsindicative of blood flow, a pulse, or movement of the cardiac wall suchas described in U.S. Pat. No. 5,824,029, the disclosure of which isincorporated by reference herein. A further technique of measuring thehemodynamic output of the patient is with the use of a pulse oximetersuch as the implantable one described in U.S. Pat. No. 4,623,248, thedisclosure of which is incorporated by reference herein.

The output of the hemodynamic sense circuit 28 is fed to a cardiacoutput detection circuit 18 which analyzes the data and determines anestimate of the cardiac output. Data from the arrhythmia detectorcircuit 20 and the cardiac output detection circuit 18 is fed to themicroprocessor 16. The microprocessor 16 determines if MVT isappropriate, and what MVT parameters to apply at the present time. IfMVT is indicated, the microprocessor 16 prompts the output control 22 tocharge a capacitor within the output circuit 26 via the capacitorcharger 24. The output control 22 directs the output circuitry 26 todeliver the pulses to the patient's upper body regions 40 via the outputleads 32. The microprocessor 16 may communicate with external sourcesvia a telemetry circuit 14 within the device 10. The power for thedevice 10 is supplied by an internal battery 12.

FIG. 2A is a diagram showing the connection of an implantable device 10′according to one embodiment to the heart as one of the regions in thepatient's upper body 40 in an epicardial patch configuration. In thisthoracotomy configuration, current passes through an output lead pair 32to electrode patches 42 which direct the current through the heart. Apressure sense lead 34 passes the signal from an optional pressuretransducer 46 which lies in the heart. The ECG is monitored by senseelectrodes 44 and passed to the device 10′ by a lead 36. The area of theelectrodes 42 is at least 0.5 cm². The size of the electrode is greaterthan that of a pacing lead and no more than that of a defibrillationelectrode or between approximately 0.5 cm² and 20 cm² each.

FIG. 2B illustrates an example of a non-thoracotomy arrangementaccording to one embodiment. In this system, the current passes from acoil electrode 52 in the heart to the housing of the MVT device 10″. Anendocardial lead 50 combines the ECG sensing lead and the pulse outputlead. The ECG is monitored by sense electrodes 44 in the heart andpasses through the endocardial lead 50. There is an optional pressuretransducer 46 in the heart which passes a signal to the device 10″ viaoptional lead 34.

FIG. 2C illustrates an implantable MVT device 10′″ that supports a setof diverse electrode arrangements for selectively applying MVT todifferent areas of the patient. In addition to electrodes 42 and 52discussed above in the thoracotomy and non-thoracotomy arrangements fordirecting the MVT through the myocardium, device 10′″ further includesadditional electrodes 58 a and 58 b for placement at specific locationsin the patient's upper body, 60 a and 60 b, to direct MVT throughnon-cardiac muscles. Examples of locations 60 a and 60 b include(without limitation) locations for activating the pectorial muscles,intercostals muscles, the diaphragm (e.g., via stimulation of thephrenic nerve), and the abdominal muscles. The additional electrodes 58a and 58 b, in various embodiments, have a variety of constructions andlocations, including, for example, subcutaneous patch electrodes, one ormore additional electronics/battery housings, intra-vascular leads, andthe like. Placements include any suitable location such as, for example,subcutaneously at the base of the neck, in the azygos vein, in thecephalic vein, subcutaneously in the lower torso, and subcutaneously onone or both sides of the upper torso.

In a related embodiment, the additional one or more of electrodes 58 aand 58 b are used for hemodynamic measurements such as, for example,electrical impedance plethysmography or tomography. In one suchembodiment, one of the additional electrodes 58 a, for instance, isimplanted high in the upper chest region or at the base of the neck,while another one of the additional electrodes, 59 a, for instance, isimplanted lower in the abdominal region. Even though electrode 58 a andelectrode 59 a may not used as a cathode/anode pair for application ofMVT (this would be the case where, for example, electrode 58 a has acomplementary electrode 58 a placed elsewhere for applying MVT to region60 a, and where electrode 59 a has a complementary electrode 59 a placedelsewhere for applying MVT to region 60 b), one of electrodes 58 a andone of electrodes 59 a can be operated as an anode/cathode pair witheach other for purposes of impedance measurement to determine bloodflow, using a suitable switching arrangement in the implantable MVTdevice 10′″.

In a related embodiment, an electrical impedance measurement isperformed using frequency division or code division multiplexingrelative to applied MVT therapy. Thus, the impedance measurement may becarried out while rejecting the interference caused by application ofthe MVT signals. This approach permits a hemodynamic impedancemeasurement to be performed without having to interrupt application ofthe MVT and without having to time the measurement to coincide with timeperiods between MVT pulse packets. Accordingly, in one embodiment, areal-time, continuous hemodynamic monitoring is performed while MVT isadministered. The blood flow can thus be plotted as a function of time,and correlated to the parameters of the MVT being applied. Thisinformation can be displayed to an operator as a chart recording ordisplayed trace, and can be automatically stored and analyzed toascertain MVT performance.

FIG. 3A is a diagram illustrating an example AED 100 that utilizes MVTaccording to one embodiment. AED 100 is can be a hand-portableinstrument that is self-powered from an optionally-rechargeable battery102. Battery 102 provides an energy source that can be converted andconditioned for powering the various circuitry of AED 100. A low voltagepower supply 104 converts the battery power into one or more stabilizedpower supply outputs 105 for supplying the power to the subsystems ofAED 100. The subsystems include a controller 106, for example amicroprocessor that is programmed and interfaced with other subsystemsto control most of the functionality of AED 100.

In the embodiments in which the controller 106 is implemented as amicroprocessor or microcontroller, the microprocessor interface includesdata and address busses, optional analog and/or digital inputs, andoptional control inputs/outputs, collectively indicated atmicroprocessor interface 107. In one example embodiment, themicroprocessor is programmed to control the sequence of theelectrotherapy, as well as the output waveform parameters. The userinput to the system can be in the form of simple pushbutton commands, orvoice commands.

Example AED 100 includes a discharge circuit 108 for administeringtherapeutic stimuli to the patient. Discharge circuit 108 controls therelease of therapeutic energy to achieve a desired stimulus having aparticular waveform and energy. Charge circuit 110 energizes dischargecircuit 108 to achieve the desired output stimulus. High voltage powersupply 112 provides a sufficient energy source 113 to charge circuit 110to enable charge circuit 110 and discharge circuit 108 to ultimatelydeliver one or more defibrillation pulses to an exterior surface of thepatient. Typically, a voltage sufficient to achieve a therapeuticdefibrillation stimulus from the exterior of a patient is in the rangeof 1 kV-3 kV.

In accordance with this embodiment, AED 100 also includes a mediumvoltage power supply 114. Medium voltage power supply 114 provides amedium voltage source 115 that enables charge circuit 110 and dischargecircuit 108 to ultimately deliver one or more MVT signals to theexterior of the patient. In one embodiment, the medium voltage powersupply is adapted to provide a regulated voltage in the range from20-1000 V.

The defibrillation and MVT stimuli are administered to the patient viapatient interface 116. In one embodiment, patient interface 116 includeselectrodes 118 a and 118 b that are adhesively applied to the patient'schest area, typically with an electrically-conductive gel. Electrodes118 a and 118 b are electrically coupled, such as by insulated copperwire leads 120, to discharge circuit 108. In one example embodiment,electrodes 118 a and 118 b can deliver the defibrillation stimuli andthe MVT stimuli as well as obtain information about the patient'scondition. For example, electrodes 118 can be used to monitor thepatient's cardiac rhythm. Signals originating in the patient that aremeasured by electrodes 118 are fed to monitoring circuitry 122.

In one embodiment, electrodes 118 a and 118 b are part of compoundelectrode patches in which each patch (having a common substrate) has aplurality of individually-selectable electrodes. In this arrangement,device 100 is programmed to select certain ones of the individualelectrodes on each compound patch to achieve a therapeutic purpose. Onesuch purpose is to activate an individual electrode that is mostoptimally placed on the patient's body for the desired MVT ordefibrillation therapy. This approach can be used to correct for thevariability in placement of the electrode patches by unskilled rescuersor even skilled rescuers working under difficult circumstances in thefield. Device 100 in this embodiment may include a switchingarrangement, either electromechanical or electronic, or may communicatecontrol information to an external switching arrangement, which may beincorporated into the compound patch. In a related embodiment, the ECGsignal strength, as measured using various pairs of the individualelectrodes of the compound patches, is used to determine the electrodesto be used for MVT and/or defibrillation administration. In anotherrelated embodiment, the hemodynamic measurement of the MVTeffectiveness, as recorded for different electrode pairs, is used as abasis for switchably selecting the electrodes to be used fordefibrillation. In yet another embodiment, certain electrodes areselected from among the plurality of electrodes on each compound patchto target specific regions to which MVT is to be applied.

In one embodiment, patient interface 116 includes an MVT effectivenesssensor 124 coupled to monitoring circuitry 122. MVT effectiveness sensor124 can measure observable patient characteristics that are related tothe patient's condition, in like fashion to the hemodynamic monitoringand determining arrangements described above for an implantableembodiment. Additional details about the MVT effectiveness monitoringare discussed below.

AED 100 also includes a rescuer interface 126 operatively coupled withcontroller 106. In one embodiment, rescuer interface 126 includes atleast one pushbutton, and a display device for indicating at least theoperational status of AED 100. In a related embodiment, rescuerinterface includes a system for providing visual or audible prompting orinstructions to the rescuer. In another embodiment, rescuer interface126 includes a plurality of human-operable controls for adjusting thevarious AED operational parameters, and a display device that indicatesmeasurements made by monitoring circuitry 122.

FIG. 3B is a diagram illustrating human interface portions of exampleAED 100′ according to one embodiment. AED 100′ is a physicalimplementation of AED 100 (FIG. 1A). AED 100′ is housed in a lightweightportable housing 130 having a base portion 132 and a hinged lid 134 inan exemplary clam-shell arrangement as illustrated, where opening andclosing of the lid turns the device on and off, as diagrammed at 136.Other embodiments do not have the base-cover arrangement, and insteadhave a housing consisting of a single enclosure, in which case thedevice has an on/off switch. The device's relatively small size andweight, and carrying handle 138 facilitate hand-portability of thedevice. Display 126 a′ may have a text only display 140 or may include agraphical display 142 that could, among other items, display an ECGwaveform. The device also has a speaker 126 b for voice prompting of theproper rescue sequence, a non-volatile readiness indicator 126 d′ thatindicates whether or not the device is in working order, an optional“shock” button 126 c′ and receptacles for the patient electrodes 118 a′and 118 b′ and an MVT effectiveness sensor 124′.

AED 100′ includes two types of patient interface. First, electrodes 118a′ and 118 b′ are adapted to be adhesively coupled to the patient'sskin. In one embodiment, the adhesive consists of an electricallyconductive gel. Electrodes 118 a′ and 118 b′ can be used to measure thepatient's cardiac rhythm, and to apply MVT and defibrillation therapy tothe patient. Second, MVT effectiveness sensor 124′ includes a transduceradapted for measuring one or more vital signs of the patient.

FIG. 3C is a diagram of several possible patient 160 connections to anAED 158 according to one embodiment including: defibrillation/ECGelectrodes 118 a′ and 118 b′, pulse oximeter 124 a′, ETCO2 sensor 124b′, Doppler or ultrasound pulse sensor 124 c′, and blood pressure sensor124 d′. More generally, the MVT Effectiveness sensor can be a variant ofany of the monitoring techniques discussed above, for instance, thepulse oximetry measurement for an external embodiment may be achievedusing a fingertip pulse oximeter as the MVT effectiveness sensor 124.Other suitable techniques for monitoring a hemodynamic state of thepatient may also be used. For instance, alternatively or in conjunction:a pulse oximeter, a sonic arterial pulse sensor, a gas sensor, or ablood pressure sensor. In another embodiment, the O₂ saturation sensor124 a′, end tidal sensor 124 b′, and pulse detection unit 124 c′, arebattery-powered and are adapted to communicate measurement data viawireless radio frequency link. For example, Bluetooth technology couldbe utilized to accomplish close-range wireless data communications.

In one example embodiment, arterial pulse activity measured from anexterior of the patient by way of pressure sensing, or by way of Dopplerultrasound technology. In one embodiment, the MVT effectiveness sensorincludes a transthoracic impedance measuring arrangement that detectschanges in the chest impedance with cardiac output. Referring again toFIG. 3B, in one embodiment, MVT effectiveness sensor 124′ is integratedwith an adhesive patch adapted to be attached to the patient's skin. Ina related embodiment, the transducer portion of MVT effectiveness sensor124′ is implemented in a thin-or-thick-film semiconductor technology.Examples of suitable sites for arterial pulse sensing include thepatient's aorta, femoral arteries, carotid arteries, and brachialarteries. Other accessible arteries may also be suitable. In one exampleembodiment of AED 100′, the measurement collected via MVT effectivenesssensor 124′ is displayed, substantially in real-time, on display 126′.The displayed measurement can be numerical or graphical, such as abar-type or chart recorder-type display.

In a related embodiment, a plurality of different techniques may be usedtogether in a more advanced AED device enabled with MVT. Such devices,with their multiple sensors to engage with the patient, may be moresuitable for use by trained rescuers, such as paramedics, for example.

In operation, AED 100 is interfaced with the patient via leads 118 a/118b, and MVT effectiveness sensor. In one embodiment, AED 100 providesguidance to a rescuer, via rescuer interface 126, for properlyinterfacing with the patient. AED 100 measures the patient's conditionusing monitoring circuitry 122 and at least a portion of the patientinterface 116. Next, AED 100 analyzes the measured patient's conditionto determine the existence of any indications for treating the patient.If the patient exhibits a condition treatable by AED 100, the devicedetermines the type of therapeutic signal to apply to the patient, andproceeds to apply the treatment. The therapeutic signal can be an MVTsignal, CPR prompt, or a defibrillation signal, either of which isdelivered via discharge circuit 108 and leads 118 a/118 b. During arescue process, AED 100 provides prompting or instructions to a rescuerfor facilitating the therapy and for protecting the rescuer's safety.

Speaking generally for both, implantable, and external MVT-equippedelectrotherapy devices, in various embodiments, a plurality of differentMVT waveforms adapted to force muscular contractions are disclosedherein. The waveforms are each adapted to repeatedly artificially forceand maintain musculature of the patient in a contracted state for a timesufficient to achieve myocardial perfusion and to subsequently cause themusculature to relax, thereby achieving a forced hemodynamic effectsufficient to reduce a rate of degradation of the patient's physicalcondition resulting from a cardiac arrhythmia.

The MVT waveforms discussed herein are administered at a higher energythan a pacing pulse, but at a lower energy than a defibrillation pulse.A pacing pulse is adapted to initiate a myocardial cell activationprocess in the heart, wherein myocardial tissue naturally contracts dueto the heart's natural activation wavefront propagation. Pacing merelyadjusts natural cardiac activity, such as electrically stimulatingcardiac muscles such that they contract synchronously across differentregions of the heart. Therefore, a pacing waveform is incapable ofelectrically forcing and/or maintaining a heart contraction or inducingcardiac perfusion during a cardiac event such as ventricularfibrillation. A defibrillation pulse, on the other hand, involves thedelivery of energy sufficient to shock the heart into a “reset state”,and is intended to reset the natural electrical activity of the heart.In contrast with pacing and defibrillation pulses, in one embodiment,the MVT waveforms as discussed herein are delivered with sufficientenergy to electrically force a cardiac contraction, however withoutdelivering energy intended to perform a cardiac “reset” such as wouldresult from a defibrillation pulse. In various embodiments, the MVTwaveforms discussed herein adapted to artificially force and maintainthe heart in a contracted state for a time sufficient to achieve cardiacperfusion.

FIG. 4A is a diagram illustrating some of the general parameters of theMVT pulse waveforms The train rate TR can be considered to be the forced“heart rate” in beats per minute, since a pulse packet produces onechest constriction. The duration is the length of time for during whicha single session of MVT is applied. FIG. 4B is a diagram detailing asingle pulse packet, having parameters of amplitude (AMP), pulse widthPW, pulse period PP, and train width TW.

Certain effective parameters have been reported in the followingpublished manuscripts, incorporated by reference herein: “TransthoracicApplication Of Electrical Cardiopulmonary Resuscitation For Treatment OfCardiac Arrest,” Crit Care Med, vol. 36, no. 11, pp. s458-66, 2008 and“Coronary Blood Flow Produced by Muscle Contractions Induced byIntracardiac Electrical CPR during Ventricular Fibrillation,” PACE vol.32, pp. S223-7, 2009.

Table 1 below provides an exemplary range of parameter valuescorresponding to empirically determined effectiveness.

TABLE 1 Exemplary Parameter Value Ranges for MVT Value of ParameterValue of Parameter Parameter (Implanted Devices) (External Devices) MVTDuration 20-120 sec. 20-120 sec. Train Rate 30-120 per min. 30-120 permin. Pulse Current 0.25-5 A 0.25-5 A Amplitude Pulse Voltage 15-250 V ?60-300 V Amplitude Pulse Width 0.15-10 ms 0.15-10 ms Pulse Period 5-70ms 5-70 ms

In a related aspect of the invention, the MVT waveform is tuned toincrease selectivity of muscle type in the application of the MVT.Muscle type selectivity permits more precise targeted treatment based onthe patient's condition, and facilitates management of muscle fatigue toprolong the MVT treatment duration.

An MVT waveform that is optimized for skeletal muscle capture (OSC)according to one embodiment is adapted to force primarily skeletalmuscle contractions. The OSC waveform is adapted to force a contractionand subsequent release of skeletal muscles in order to achieve perfusionof the heart and other vital organs, and can force some amount ofventilation.

An MVT waveform that is optimized for myocardial capture (OMC) accordingto a related embodiment is adapted to force cardiac muscle contractions.The OMC waveform is adapted to force contraction of primarily cardiacmuscles in order to achieve some level of perfusion for the heart andother vital organs. Tables 2 and 3 below provide exemplary ranges forOSC and OMC MVT parameter values; whereas tables 4 and 5 below providean exemplary optimal set of values for OSC and OMC waveforms,respectively.

TABLE 2 Example Ranges of Optimal OSC Parameter Values. VariableParameter Optimal Range Pulsed Output 75-300 V (external); Voltage 20-80V (implantable) Pulsed Output 1-5 A Current Pulse Width .10-.25 ms PulsePeriod 10-20 ms Duration 10-30 seconds Packet Width 100-300 ms TrainRate 80-160 bpm

TABLE 3 Example Ranges of Optimal OMC Parameter Values. VariableParameter Optimal Range Pulsed Output 75-300 V (external); Voltage 20-80V (implantable) Pulsed Output 1-5 A Current Pulse Width 5-10 ms PulsePeriod 20-40 ms Duration 10-30 seconds Packet Width 100-300 ms TrainRate 80-160 bpm

TABLE 4 Exemplary Stimulation Waveform for OSC Variable ParameterOptimal Value Pulsed Output 75-300 V (external); Voltage 20-80 V(implantable) Pulsed Output 2 A Current Pulse Width 7.5 ms Pulse Period30 ms Duration 20 seconds Packet Width 200 ms Train Rate 120 bpm

TABLE 5 Exemplary Stimulation Waveform for OMC Variable ParameterOptimal Value Pulsed Output 75-300 V (external); Voltage 20-80 V(implantable) Pulsed Output 2 A Current Pulse Width .15 ms Pulse Period15 ms Duration 20 seconds Packet Width 200 ms Train Rate 120 bpm

In one type of embodiment, the waveform parameters are varied ormodulated for different purposes. One such purpose is to enhance oradjust the MVT effectiveness—that is, to vary the hemodynamic and otherelectrostimulation effects to achieve one or more treatment goals. Onesuch treatment goal is management of muscle fatigue. MVT stimulationcan, in a matter of a few minutes, fatigue the heart or other muscles toa point where they become unresponsive to further stimulation.Accordingly, in this embodiment, the MVT parameters are set or adjustedto minimize, or simply reduce, MVT-induced muscle fatigue, therebyallowing the MVT treatment to be prolonged.

In one example embodiment, the MVT-enabled implantable or externalelectrotherapy device uses its hemodynamic monitoring facilities tomeasure variables such as blood flow, blood pressure, or bloodoxygenation, or a combination thereof. Using this measured information,the intensity and targeting of the MVT is adjusted. To illustratetargeting, in one specific example, when the monitored hemodynamicoutput from MVT stimulating the heart with an OMC waveform begins todecrease, the MVT circuit responds to the reduction by switching to aOSC waveform to stimulate the non-cardiac muscles and give the heart theopportunity to rest and either conserve or restore its ATP stores. Toillustrate adjustment of MVT intensity, the pulse amplitude, or pulseperiod (or both) are adjusted to reduce the degree of stimulation beingapplied while the hemodynamic condition is monitored. In one situation,the MVT intensity is reduced to a minimum level where the hemodynamicoutput is still adequate. This reduction in intensity reduces musclefatigue effects and preserves battery life of the device, which alsoprolongs the MVT treatment duration that is possible.

In a related example, for a device that performs defibrillation therapy,the controller is programmed to adjust the MVT parameters to improve thelikelihood of successful defibrillation. Accordingly, in thisembodiment, as the time to administer the defibrillation shockapproaches, the MVT-enabled defibrillator switches to the OSC waveformfor stimulating primarily non-cardiac muscles. This gives the heart moretime to rest, and to be in a “fresher” state for receiving thedefibrillation therapy, which improves the likelihood of successfulconversion of the arrhythmia with defibrillation.

In another embodiment, for either the OSC, or OMC waveforms, or inanother type of MVT waveform which may be non-targeted to muscle groups,the pulse period is modulated during administration of the MVTadministration. The degree of modulation can be in the neighborhoods of5%, 10%, 15%, or more. In one variant of this embodiment, the modulationis randomized, or noise-like. In another embodiment, the modulation isapplied with a certain pattern (i.e., with a predetermined modulatingsignal), or with a certain combination of patterns, which can bealternated based on randomization or based on one or more alternationfunctions. Modulation of the pulse period in any of these fashions mayhelp to recruit more muscle fibers than a MVT signal with non-modulatedpulse period, and may reduce or delay the onset of muscle fatigue causedby MVT. Additionally, the modulation of pulse period may enhance thehemodynamic effect, which in turn permits a reduction in pulse amplitudefor an equivalent hemodynamic output or sympathetic stimulation effect.

In a further aspect of the invention, the various electrodes describedabove for MVT administration can be selectively switched in and out ofthe pulse generating circuitry, enabling selective application of MVT tospecific regions of the body (corresponding to specific muscles ormuscle groups). Table 6 below lists various exemplary muscles that areindividually targeted in one type of embodiment.

TABLE 6 Exemplary Muscles Targeted through Specific MVT ElectrodePlacement Muscle ID Muscle Description A Heart B Right Pectoral C LeftPectoral D Right Intercostals E Left Intercostals F Right Abdominals GLeft Abdominals

In one type of embodiment according to this aspect of the invention, thetargeting of muscles is automatically coordinated and varied based onchanging circumstances, by the MVT-enabled device, to achieve a desiredtherapeutic effect based on the monitored patient condition, includingthe type of arrhythmia, the hemodynamic effect of applied MVT, and onthe specific treatment or rescue algorithm being administered. In arelated embodiment, the targeting of specific muscles is coordinatedwith the MVT waveform to be applied to further enhance the specificityof the MVT targeting.

One example of the desired therapeutic effect is management of musclefatigue. In a corresponding embodiment, certain muscles are stimulatedby MVT for longer or shorter durations based on that muscle's enduranceof MVT. In a related embodiment, muscle groups having left and rightsides, i.e., pectorals, intercostals, abdominals, are stimulated suchthat only one side at a time is activated by MVT, allowing the otherside to rest and recuperate. Variation of muscle selection can bepredetermined according to a programmed algorithm which is selected inresponse to the detected type of arrhythmia. Alternatively, to accountfor variation among patients, selection of muscles for stimulation ismade in response to hemodynamic monitoring.

In one embodiment, the controller of the MVT circuit maintains a one ormore data structures that relate the different muscles for which thedevice is configured to stimulate via MVT, to amplitude and waveformparameter information corresponding to that muscle group. In a relatedembodiment, the data structure(s) further include associations betweentreatment algorithms corresponding to various arrhythmias or patientconditions, as measured by the patient monitoring facilities of thedevice, and MVT parameter values to use for those arrhythmias orconditions.

In one example, the device is programmed to apply relatively higherintensity MVT to one type of muscle group (or one side of the body) thanto another muscle group or side of the body as a test of endurance ofthe patient's musculature to MVT. The other side, which is lessintensely stimulated, may then remain available for longer-duration MVTtherapy.

In another embodiment, the device is configured with an algorithm toapply MVT as a test stimulus to assist in diagnosis of the patient'scondition or in adjustment of the MVT parameters in order to providebetter patient-specific treatment. In one example of such an embodiment,the hemodynamic monitoring includes both, blood flow information, andblood oxygenation information. MVT is applied to force perfusion andventilation, and the hemodynamic condition is monitored. The presence ofadequate blood flow being generated by the MVT, as measured by the bloodflow monitoring, while the blood oxygenation reads lower than expected(based on baseline data stored in the device corresponding to theduration of the patient's arrhythmia and amount of flow measured),suggests that the patient is not achieving sufficient respiration.Accordingly, in this embodiment, the MVT is adapted to increase theproportion of time or degree of stimulation targeting muscles thatprovide a ventilation effect. Thus, for instance, the MVT may be adaptedto stimulate the phrenic nerve for a longer period (to thereby cause thediaphragm to contract for a longer time, causing a larger breath to beforced).

In another example, hemodynamic monitoring is configured to distinguishbetween forced pulse output and return. In one particular embodiment,the device is configured to first test for a weak return, then test fora weak pulse. An indication of weak return but adequately high pulsepressure suggests that the heart is having difficulty expanding to fillwith blood (e.g., tamponade). Accordingly, the MVT is automaticallyadapted to enhance and prolong the targeting of muscles that tend toexpand the chest cavity, thereby lowering pressure around the heart tohelp draw in more blood. In another example, a strong return but weakpulse indicates that the heart is likely to have become distended. Inresponse, the MVT is adapted to optimize contraction of the distendedheart, such as, for instance, extending the duration of the pulsepackets to force the heart to stay contracted for a longer period oftime. Alternatively, or additionally, an OSC waveform can besynchronized with an OMC waveform such that one immediately follows theother. Thus, the heart can be compressed for an extended period by firstcapturing myocardial cells to contract, then by squeezing the heartusing the skeletal muscles.

In yet another specific example of this aspect of the invention,hemodynamic monitoring is combined with ECG monitoring and MVT toidentify and treat PEA. In this example, PEA is detected by the absenceof hemodynamic output while the ECG measurement indicates the presenceof a heart rhythm. In this condition, MVT is applied in synchronousfashion with the ECG. In one case, MVT is applied such that the forcedcontraction and permitted relaxation of the heart coincides with the QRScomplex, thereby forcing the heart to beat as if the ECG and themechanical action were normal. In another case, MVT is applied at aspecific offset angle relative to the normal QRS complex and mechanicalaction. In a related case, the MVT is applied sequentially at a seriesof specific offset angles for each ECG cycle.

Another aspect of the invention is directed to a multi-tier MVTtreatment algorithm, to be carried out by an implantable or externalMVT-enabled device. The device according to one embodiment is configuredto apply a higher intensity MVT at certain stages of rescue or lifesupport, and to apply a lower intensity MVT at other stages. Theintensity of MVT is varied by adjusting certain MVT parameters. For MVTwaveforms targeting skeletal muscle, the pulse period is primarilyvaried to control the intensity of muscle contraction. For MVT waveformstargeting primarily the myocardium, the amplitude is the parameterprimarily responsible for the MVT intensity. To a lesser extent, thepulse period may also be adjusted to control OMC intensity.Higher-intensity and lower-intensity MVT may be selectively applieddifferently between MVT targeting the heart and MVT targeting theskeletal muscles, depending on the treatment objective, which in turndepends on the detected patient condition obtained using the patientmonitoring facilities of the device. Thus, for example, in certaincircumstances, high-intensity MVT may be applied to skeletal muscleswhile low-intensity MVT is applied to the myocardium, and vice-versa.

In one embodiment, selection of high-intensity and low-intensity MVT isbased in part on the duration of the arrhythmia, and on the currentpoint in the treatment protocol. For example, in the case of a patientcondition treatable with defibrillation or cardioversion, the MVTprotocol requires high-intensity MVT prior to the shocks for convertingthe arrhythmia. More intensive MVT in this case places the heart in abetter condition to respond favorably to the defibrillation orcardioversion. A refinement of this approach in a related embodimentdistinguishes between MVT targeting the myocardium and MVT targetingskeletal muscles. In this refined approach, as discussed above, themyocardium is progressively given reducing-intensity MVT as the time todefibrillate approaches, while the skeletal MVT remains at ahigh-intensity. This improvement allows the heart to recover from theMVT. The reduced-intensity MVT applied to the heart may also be adjustedto optimize sympathetic stimulation (again, facilitating betterdefibrillation success) while reducing the MVT energy applied to forcecontraction, which fatigues the heart.

In a related embodiment, if defibrillation is unsuccessful following thestandard protocol of 4-6 shocks, the MVT for both, the heart and theskeletal muscle, is automatically adjusted to their respectivelow-intensity modes so that the patient's life support can be prolongedwith MVT. This becomes essentially a muscle fatigue management (anddevice energy conservation) strategy.

In another aspect of the invention, adaptive MVT is applied to supportpatients in non life-critical conditions but where the heart may benefitfrom a certain level of assistance. Hemodynamic monitoring and ECGmeasurements are used to identify such conditions, and to control properadministration of the MVT. In one such condition, orthostatichypotension, an omni-directional accelerometer is included in thedevice, and is configured with the measuring circuitry and decisionlogic to detect blood pressure relative to movement and orientation ofthe patient. Thus, when the patient is standing up from a seated orreclined position, and when the patient's blood pressure fails torespond to accommodate such movement, MVT may be applied to assist theheart to develop more pressure. In one specific embodiment, the MVT forthis application targets the myocardium, with a specific OMC waveform toreduce the discomfort the patient may experience due to inadvertentstimulation of skeletal muscle.

The embodiments above are intended to be illustrative and not limiting.Additional embodiments are within the claims. In addition, althoughaspects of the present invention have been described with reference toparticular embodiments, those skilled in the art will recognize thatchanges can be made in form and detail without departing from the spiritand scope of the invention, as defined by the claims.

Persons of ordinary skill in the relevant arts will recognize that theinvention may comprise fewer features than illustrated in any individualembodiment described above. The embodiments described herein are notmeant to be an exhaustive presentation of the ways in which the variousfeatures of the invention may be combined. Accordingly, the embodimentsare not mutually exclusive combinations of features; rather, theinvention may comprise a combination of different individual featuresselected from different individual embodiments, as understood by personsof ordinary skill in the art.

Any incorporation by reference of documents above is limited such thatno subject matter is incorporated that is contrary to the explicitdisclosure herein. Any incorporation by reference of documents above isfurther limited such that no claims included in the documents areincorporated by reference herein. Any incorporation by reference ofdocuments above is yet further limited such that any definitionsprovided in the documents are not incorporated by reference hereinunless expressly included herein.

For purposes of interpreting the claims for the present invention, it isexpressly intended that the provisions of Section 112, sixth paragraphof 35 U.S.C. are not to be invoked unless the specific terms “means for”or “step for” are recited in a claim.

What is claimed is:
 1. A method for treating arrhythmia in a patientusing an electrotherapy device, the method comprising: providing apatient interface, including a plurality of electrodes and at least onehemodynamic sensor, placed in electrical contact with the patient;generating medium voltage therapy (MVT) via the patient interface as aconfigurable waveform having a set of adjustable waveform parameters,wherein the waveform is defined by series of pulse trains having anadjustable train repetition rate, the pulse trains being composed ofpulses having an adjustable pulse width, an adjustable pulse period, andan adjustable pulse amplitude, the MVT being of an energy levelinsufficient to shock the heart into a reset state; monitoring thepatient via the patient interface for an occurrence of an arrhythmia;monitoring a hemodynamic condition of the patient via the patientinterface; based on the arrhythmia monitoring and on the hemodynamiccondition monitoring, ascertaining a patient condition that is treatableby the MVT; based on a treatment or life-support objective correspondingto the patient condition treatable by the MVT, initiating application ofthe MVT to the musculature of the patient via the patient interface totarget a selected muscle group, wherein the selected muscle group isrepeatedly (a) forced into a contracted state, (b) maintained in thecontracted state for a time sufficient to achieve myocardial perfusion,and (c) thereafter allowed to relax, thereby achieving a forcedhemodynamic effect sufficient to reduce a rate of degradation of thecondition of the patient; adjusting the waveform parameters infurtherance of the treatment or life-support objective such that: inresponse to a measured level of cardiac output during application of theMVT targeting a selected first muscle group exceeding a minimal leveladequate for the treatment or life-support objective, reducing anintensity of MVT stimulation targeting the first muscle group; inresponse to a measured reduction of level of cardiac output duringapplication of the MVT targeting a selected first muscle group,targeting a selected second muscle group distinct from the first musclegroup with the MVT having adjusted waveform parameters corresponding tothe second muscle group.
 2. The method of claim 1, wherein reducing theintensity of the MVT and targeting of the second muscle group areperformed to reduce muscle fatigue in the first muscle group caused bythe MVT.
 3. The method of claim 1, wherein in initiating application ofthe MVT and in targeting the MVT to the second muscle group, the firstmuscle group consists of primarily myocardial musculature and the secondmuscle group consists of primarily skeletal musculature.
 4. The methodof claim 1, wherein in initiating application of the MVT and intargeting the MVT to the second muscle group, first muscle groupconsists of primarily myocardial musculature and the second muscle groupconsists of primarily musculature of the diaphragm.
 5. The method ofclaim 1, wherein the targeting of the second muscle group is achieved byapplying the MVT with a set of adjusted waveform parameters adapted tomore efficiently stimulate to the second muscle group.
 6. The method ofclaim 1, wherein in providing the plurality of electrodes, the pluralityof electrodes includes electrodes positioned at various regions of thetorso of the patient, and wherein initiation of the MVT includesselectively applying the MVT to specific one or more regions viaselected groupings of the plurality of electrodes such that variousdifferent muscle groups of skeletal musculature are selectivelytargeted, and wherein the first muscle group and the second muscle grouprespectively correspond to different regions of the torso of thepatient.
 7. The method of claim 6, further comprising: maintaining atleast one data structure that relates each of the different musclegroups to amplitude and waveform parameter information corresponding tothat muscle group, wherein different muscle groups correspond todifferent waveform and amplitude characteristics.
 8. The method of claim6, wherein one of the muscle groups consists of skeletal muscles on theleft side of the patient, and another one of the muscle groups consistsof skeletal muscles on the right side of the patient.
 9. The method ofclaim 6, wherein one of the muscle groups consists of abdominal muscles,and another one of the muscle groups consists of intercostals muscles.10. The method of claim 1, further comprising: providing a high voltagetherapy (HVT) pulse generator operatively coupled to the patientinterface and adapted to supply the HVT via the patient interface,wherein the HVT is of an energy level sufficient to shock the heart intoa reset state; and based on a treatment or life-support objectivecorresponding to the patient condition treatable by the HVT, applyingthe MVT targeting primarily myocardial musculature at a progressivelyreducing intensity as a time at which the HVT is to be appliedapproaches; targeting skeletal musculature at high intensity with theMVT as the time at which the HVT is to be applied approaches; andthereafter, applying the HVT to the patient via the patient interface.11. The method of claim 1, further comprising: measuring at least onehemodynamic condition selected from the group consisting of: blood flow,blood pressure, blood oxygenation, or any combination thereof.
 12. Themethod of claim 1, wherein monitoring the patient further comprises:distinguishing between hemodynamic conditions of forced pulse output andreturn, and adjusting the MVT parameters in response to detecteddifferences in the hemodynamic conditions of forced pulse output andreturn.
 13. The method of claim 12, further comprising: in response toan indication of weak return but adequately high pulse pressure to meetthe treatment or life-support objective, adjusting the MVT to enhanceand prolong the targeting of muscles that tend to expand the chestcavity, thereby lowering pressure around the heart to help draw in moreblood; and in response to a strong return but weak pulse, adjusting theMVT to extend the pulse train duration to force the heart to staycontracted for a longer period of time.
 14. The method of claim 1,further comprising: modulating the pulse period of the MVT.
 15. Themethod of claim 1, wherein monitoring the patient includes detectingpulseless electrical activity (PEA) in the patient, and responding todetection of PEA by causing the electrotherapy circuit to apply MVTsynchronized with a measured electrocardiogram (ECG) signal.
 16. Themethod of claim 1, wherein in generating the MVT, the train repetitionrate is adjustable within the range of 30 and 120 per minute, the pulsewidth is adjustable within the range of 0.15 and 10 milliseconds and anthe pulse period is adjustable within the range of 5 and 70milliseconds.
 17. The method of claim 1, wherein in generating the MVT,a pulse current of the MVT delivered to the patient falls within therange of 0.25 and 5 amperes.
 18. The method of claim 1, wherein, ingenerating the MVT, a first MVT waveform is generated targeting thefirst muscle group and, immediately thereafter, a second MVT waveform isgenerated targeting the second muscle group such that the musculature ofthe first muscle group and the second muscle group continuously maintaincompression of the heart.